Scotland Island is not connected to the mains sewer. This means all houses have an on-site sewerage disposal system. This can be in the form of a septic tank and absorption trenches or an aerated system and irrigation release or some hybrid of the above.  

Some work has been done to identify future viable solutions and engage with the NSW Government. This information is available on the SIRA & Wastewater page Scotland Island Sewerage 

Care & maintenance of on-site sewerage disposal systems (septic tanks, trenches and other wastewater treatment systems)

Many factors may contribute to septic/wastewater system failure, including:

  • too much wastewater, especially in surges
  • using chemicals which kill decomposing bacteria in the system e.g. disinfectants, detergents, bleaches (minimal use is recommended)
  • extended periods of rainfall
  • excessive shadowing or compacting of the evapo-transpiration area
  • leaking plumbing which overloads the system
  • tree roots growing into and plugging trenches
  • inadequate disposal area


 Any system that stores, treats or disposes of sewage on a site must be maintained in a manner that ensures no impact occurs to public health and the environment. These systems are all classified as on-site sewage management systems and require approval to operate under the Local Government Act 1993.

Your system must be licensed with Northern Beaches Council and inspected and amended as required by the Council inspector. Those notifications of inspection will come to you by mail.

The transition from the former Pittwater Council to the Northern Beaches Council has seen some changes to the way the inspections were done. It has also further highlighted the challenges in operating those systems on Scotland Island. 

Septic systems and aerated wastewater treatment systems do not have the same maintenance requirements.  Aerated wastewater treatment systems must be inspected by an approved company every three months to maintain sufficient chlorine in the system and ensure the system is working satisfactorily. 

System maintenance

Septic tanks produce a sludge that collects on the bottom of the tank and a floating scum on the surface of the liquid.

It is important to keep the septic healthy. The Easy Septic Guide published by the NSW Office of Local Government includes a lot of great advice on how to keep your septic system in good health. 

The primary septic tank may require a pump-out (often every five to ten years, depending on the load). Failure to clean out a tank when required may cause scum to be carried out of the primary tank and into the disposal system which can then block the infiltration field. 

More information: 

 Cleaning products

Check the labelling on all household cleaning and washing products:

  • The best choice are detergents that are phosphate—free with no boron compounds and low sodium.
  • Extra phosphates and boron damage native plants and encourage excessive weed growth.
  • Salts change the structure of the soil so that it becomes less permeable.
  • Sodium levels are generally much higher in non-concentrated powders and brands that advertise their ‘softening powers.’


Some plants like wetter spots, so areas downgradient of absorption trenches can be quite well suited for those. Be mindful when gardening that products grown in the garden above or downgradient an on-site sewage system release may not be fully safe for human consumption.